Chromosoma (Berl.) 27, 86--94 (1969)

A Karyological Study of Three Species of Scincidae (Reptilia)

ROMANO DALLAI and MARIA VEGNI TALLURI Istituto di Zoologia ed Istituto di Anatomia comparata

dell'Universit& di Siena

Received February 14, 1969 / Accepted March 14, 1969

Abstract. In this paper the Authors deeribe the karyogram of three species of Scincidae (Chalcides chalcides chalcides, Chalcides ocellatus tiligugu, and Mabuya striata). The diploid number of these species is 2n = 28. I t is not possible to sub- divide the chromosome set in micro- and macrochromosomes or to recognize the heterochromosomes morphologically. Ch. ocellatus and M. striata have very similar karyograms; that of Ch. ch. chalcides is different in that chromosomes 6, 7, 8, 9, and 10 are acrocentrie. Pericentric inversion is probably involved in the karyotypic evolution of these species.

Introduction

The new techniques for karyological research developed about 12 years ago have led to a much more accurate knowledge of reptile karyo- types, and in certain cases have clearly demostra ted tha t one or the other sex is heterogametic.

I n fact, Kobel (1962, 1963), Begak, Be~ak and Nazare th (1962) and Begak (1967) have found female d igamety in various families of snakes (Viperidae, Colubridae), whereas Gorman and Aktins (1966) and Gorman, Atkins and t tolzinger (1967) as well as Cole, Lowe and Wright (1967) suspect t h a t there is male he te rogamety in some saurians of the family Iguanidae.

For two other families of saurians, Chamaeleontidae and Lacertidae, (see Matthey, 1957; Dallai and Baroni Urbani, 1967 respectively) there also exists sat isfactory karyological informations and it is certain tha t these families do not present morphological ly recognizable digamety.

On the other hand, the karyological information on the Scincidae is ou tda ted and incomplete (see Makino, 1951). I t is restricted to only four species, Scincus o//icinalis, Chalcides tridactylus, Eumeces latis- cutatus, Mabuya macularia.

We have thus under taken the re-examinat ion of one of these species as well as the examinat ion of two other Scincidae.

Karyology of Three Species of Scincidae 87

Materials and Methods

The species examined were Chalcides chalcides (L.) (~ Chalcides tridactylus), ssp. chalcides (2 male and 2 female specimens from the countryside near Rome), Chalcides oceUatus (FSrskal) ssp. tiligugu (Gmelin) (2 male and 2 female specimens from the countryside near Catania) and Mabuya striata (Peters) (1 female specimen from the National Park of Kamande, Kenya-Uganda).

Mitotic metaphases were obtained from preparations of spleen, bone marrow and blood. For spleen and bone marrow material we used the techniques described by DMlai and Baroni Urbani (1967). For the blood cells we used the following technique: blood, obtained by decapitating the specimens, was suspended in a hypotonic solution (1% sodium citrate), centrifugated for about 5 minutes, and fixed in a 3 : 1 mixture of ethanol and glacial acetic acid, after which it was resus- pended and centrifugated twice more. Smears were made with the final suspension and stained with an 8 % Giemsa solution for 8--10 hours.

In order to study meiotic phases, squash preparations of testicles were made following the techniques described in the paper by Dallai and Baroni Urbani (1967).

Twenty mitotic metaphases were drawn and photographed for each species. Measurements of the chromosome lengths were made on photographs of the same enlargement and for each chromosome pair the arithmetic mean and its standard deviation was then calculated.

Observations

Chalcides chalcides chalcides, 2n ~ 28 (Fig. 1)

I l l l o , , , , ,

5 10 I/+

Fig. l. Chalcides chalcides chalcides. Idiogram

We divided the pairs of chromosomes into four groups according to

their length and the posit ion of the eentromere (Fig. 2). The rat io of the largest chromosome to the smallest is 10.26/0.92 = 11.

Because of this rat io and the absolute dimensions of the smaller chromosome ( ~ 1 ~), we do not th ink they can be classified as micro-

chromosomes.

Group I. Consists of the four largest pairs of chromosomes. Chromo- some pair 1 is metacentr ic and has a mean length of 10.26 ~. The mean length of chromosome pair 2 is 9.87 ~. I t is sl ightly submetacentr ic and the a rm ratio is 5.57/4.50 = 1.19.

88 1%. DALLAI and M. V. TALLURI

Fig. 2. Chalcides chalcides chalcides. Chromosomes arranged in order of size

Chromosomes pairs 3 and 4 are both metacentric. Their respective lengths are 9.77 and 8.58 ~.

Group II . Only one 4.47 ~ long chromosome pair (5) was placed in this group because of the evident gap between its size and tha t of chromo- somes 4 and 6, which are 8.58 ~ long and 3.02 ~ long respectively.

Group I I I . Contains five pairs of chromosomes (6--10), all telocentric or subtelocentric. Their mean lengths decrease gradually from 3.02 (chromosome 6) to 1.45 ~ (chromosome 10).

Group IV. Consits of four more or less metacentric pairs of chromo- somes (11--14). Their lengths decrease gradually from 1.35 ~ (11) to 0.92 ~ (14).

No tetrads with the characteristics of sex chromosomes could be ob- served in meiotic figures (prepared from testes). We must therefore conclude tha t morphologically recognizable heterochromosomes are lacking in this species.

Karyoiogy of Three Species of Scincictae 89

Chalcides ocellatus tiligugu, 2n = 28 (Fig. 3)

The 14 pairs of chromosomes were divided according to length and position of eentromere into four groups (Fig. 4). The ratio between the largest and smallest chromosomes is 9.78/1.16 y, = 8.4.

I l lIl '"" 5 10 l&

Fig. 3. Chalcides ocellatus tiligugu. Idiogr~m

Fig. 4. Chalcides ocellatu8 tiligugu. Chromosomes arranged in order of size

Group I. Contains the four largest chromosome pairs. The first pair is exact ly metaeentr ic and 9.78 ~ long. Chromosome pairs 2 is submeta- eentrie, 9.04 ~ long, and has an a rm ratio of 5.64/3.40 ~ = 1.65. Chromo- some pairs 3 and 4 are both metacentr ic and are 8.36 and 7.96 ~ long

90 l~. DALLAI and M. V. TALLURI:

respectively. It is noteworthy that quite frequently the chromosomes of this group become narrower near the centromere.

Group II. A single metaeentric chromosome pair (5) has been placed in this group because its length is considerably different from that of chromosome pairs 4 and 6. In fact, it is 4.70 ~, and the other two are 7.96 ~ and 3.58 ~ respectively.

Group III. Includes chromosome pairs 6 through I0, all more or less metacentric. Their lengths decrease gradually from 3.58~ to 2.16~.

The chromosomes of pair 8 generally show negative heteropycnosis near the eentromere, indicating that they are probably nucleolar chromosomes.

Group IV. Consists of four pairs of small chromosomes (11--14) with lengths decreasing regulary from 1.74 to 1.16 ~. All four are more or less metacentric with arm ratios of 1.3, 1.3, 2 and 1.5 respectively.

As in the preceeding species, sex chromosomes can not be distinguished in the meiotic figures (spermatogenesis).

Mabuya striata, 2 n ~- 28 (Fig. 5)

Since our study of this species was limited to a single female specimen, the karyological information obtained is not very complete.

5 10 15

Fig. 5. Mabuya striata. Idiogram

There are 14 pairs of chromosomes in the somatic metaphases (Fig. 6).

The ratio between the largest pair and the smallest is 11.58/1.26 ~ = 9.1. Here too, therefore, given the absolute and relative sizes of the smallest chromosomes, we do not think they can be considered micro- crolIlosomes.

The first four pairs are morphologically identical to those of the species described above.

Chromosome pair 5 is much smaller than the preceeding one. It is 4.5 ~ long as opposed to 8.0 ~.

The sixth pair is 3.5 ~ long and therefore so much smaller than the fifth pair to justify placing the latter in a group by itself as in the other species.

Karyology of Three Species of Scincidae 91

Fig. 6. Mabuya striata. Chromosomes arranged in order of size

The remaining chromosomes (6--14) decrease in size quite regularly. Chromosome pairs 6 through 12 are clearly metacentric and pairs 13 and 14 also seem to be metacentric, but we are not certain of this.

Discussion

The karyogram of Chalcides ch. chalcides consists of 10 metacentric macrochromosomes, l0 acrocentric middle-sized chromosomes (6--10) and 8 small metacentric or submetacentric chromosomes. Our obser- vations show tha t the karyogram of Chalcides ch. chalcides is rather dif- ferent from the one described by Mat they (1933) for Chalcides tridactylus ( ~ Chalcides chalcides). In fact, Mat they describes a chromosome comple- ment of 2 n --~ 28, in which 8 chromosomes are metacentric and all the others are telocentric.

We maintain tha t the differences between Matthey 's results and ours are not due to differences in race but to the greater accuracy yielded

92 ~. I)ALLAI and M. V. TALLURI:

by modern techniques as opposed to those of the renowned Swiss cytologist. In fact, the differences concern chiefly the smaller chromo- somes.

The karyogram of Chalcides ocellatus tiligugu is clearly different from tha t of the above-mentioned species because of the median or submedian rather than terminal or subterminal centromeres in chromosome pairs 6 through 10.

The karyotype of Mabuya striata hardly differs at all from that of Chalcides ocellatus if we overlook the uncertainties regarding chromosome pairs 13 and 14. On the other hand it differs substantially from tha t of Mabuya macularia, which was studied by Asana and Mahabale (1943, cited by Makino, 1951). These authors at tr ibute a diploid chromosome complement of 26 to it, with 10 metacentric and 16 acrocentric chromo- somes, whereas Makino and Asana (1950, see Makino, 1951) correct the diploid number to 32. On the other hand Goin and Goin (1962) like report tha t M. macularia has a diploid complement of 26.

t%egarding the other Scincidae studied to date, Eumeces latiscutatus (Nakamura, 1931) has 2 n ~ 26 chromosomes, with 12 metacentric and 14 acrocentric macrochromosomes. Scincus o//icinalis (Matthey, 1933) has 2 n ~-- 32 chromosomes, with 4 metacentric and 28 acrocentric macro- chromosomes.

According to Matthey (1945) and White (1954), when there is diver- sity in the number and morphology of the chromosomes of species tha t arc systematically related, but at different evolutionary levels, the more advanced species show an increase in metacentric chromosomes at the expense of the telocentric ones. Thus evolutionary progression implies an over-all reduction in chromosome number due to the Robertsonian mechanism of centric fusion and loss of centromeres.

In our case this rule does not apply. The number of chromosome arms, or fundamental number (F.N.) for Chalcides tridactylus ( z Chal- cides chalcides) was calculated by Matthey (1933) as 48, but our results indicate tha t the number 46 is preferable. How can we explain the passage from this situation to tha t of Calcides ocellatus and Mabuya striata in which the number of chromosomes is identical but N.F. ~ 56 ?

We would suggest tha t the karyotypic evolution of these Scincidae involved pericentric inversion.

In fact, when we compare the mean lengths of corresponding chromo- somes in the different species (Fig. 7), we can see tha t they are very similar, indicating tha t chromosome fragments have not been lost. How- ever, realizing tha t any generalizations are premature, we propose to study the question more thoroughly in the future.

Karyology of Three Species of Scinciclae 93

l~egarding sex chromosomes, our da ta are sufficient to establish tha t

there is no morphologically recognizable d igamety in two species of Chalcides.

Regarding the size of the ehromosomes, it is no tewor thy t ha t among these Scincidae there is no division of the chromosome complement into macro- and mierochromosomes as in so m a n y other reptiles and

t 13 12 11

d 10- u1 9- +1 ::L. 8

6. }s (D -~ &

3 2 1

+ t.TI+ +t +tt+++

.t+ +++ +++ +r ,++ +,+ ,++ +o+

1 2 3 z~ 5 6 7 8 9 10 11 12 13 14 Haptoid chromosome number

Fig. 7. Mean length • S. D. of chromosomes of three species of Scincidae. �9 Chalcidcs chalcides chalcides; [] Chalcides ocellatus tiligugu; @ Mabuya striata

birds. We cannot say whether this denotes a lower degree of specializa- tion un t i l we unde r s t and the causes of this phenomenon.

Acknowledgements. We are most grateful to Professors B. Baecetti, P. Omodeo and D. Quattrini for their advices and critical examination of the manuscript, to Mr. E. Burroni for technical help, and Mr. S. Bruno for furnishing the specimens.

References

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94 1%. ])ALLAI and M. V. TALLURI: Karyology of Three Species of Scincidae

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Dr. Romano Dallai Istituto di Zoologia V. Mattioli 4 53100 Siena I taly

Dr. Maria Vegni Talluri Istituto di Anatomia Comparata V. delle Cerchia 5 53100 Siena I ta ly